After nearly a year in orbit, America's space-endurance champ, Scott Kelly, is just a few days away from returning to Earth — and he can't wait.

Kelly held his final news conference from the International Space Station on Thursday.

He told reporters that space is a 'harsh environment,' and you never feel perfectly normal.

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Kelly held his final news conference from the International Space Station, telling reporters that space is a 'harsh environment,' and you never feel perfectly normal.'

SCOTT KELLY AND THE TWIN STUDY

Scott Kelly, together with cosmonaut Mikhail Kornienko, boarded the ISS in March last year as part of a first-of-its-kind experiment to test how the human body copes with prolonged space travel.

They will be the first astronauts to spend a year on the station.

Mr Kelly's identical twin Mark has remained on Earth, allowing Nasa to examine the changes between these genetically identical people in two vastly different environments.

Both the Kellys will be subjected to 10 experiments in human physiology, behavioural health, microbiology and molecular.

By staying on the station for 12 months, the astronauts will provide key information on how an eventual Mars mission - estimated to last three years there and back - might play out.

From a hygiene perspective, he said, he feels as if he has been camping in the woods for a year.

From a physical point of view, though, he feels 'pretty good.'

The toughest part? Being isolated from loved ones, a situation that will pose even more of a challenge for astronauts sent to Mars.

Despite all this, Kelly said he could go another 100 days or even another year 'if I had to.'

By the time he comes home, he will have spent 340 consecutive days aloft, a U.S. record.

The world record is 438 days, set by a Russian cosmonaut in the 1990s.

Even that will pale in comparison to a Mars expedition, expected to last two to three years round trip.

Scientists hope to learn much from Kelly's mission to pave the way to Mars in another two decades; they also will collect data from his Russian roommate for the year, Mikhail Kornienko.

Along with Kornienko, Kelly will check out of the space station Tuesday, riding a Russian capsule back to the planet to end NASA's longest space flight. They will land in Kazakhstan. Then Kelly will be hustled home to Houston.

The 52-year-old astronaut said he can't wait to jump in his pool and dine at a real table with friends and family.

Kelly rocketed away last March on a research-packed mission, leaving behind two daughters and his girlfriend. He lightened things up recently by donning a gorilla suit — a gag gift from his identical twin, retired astronaut Mark Kelly — and cavorting through the station.

The brothers hope to go fishing in Alaska once things settle down.

ISS commander Scott Kelly has entered the record books by spending the most cumulative days in space for any US astronaut.

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The Nasa astronaut has been in space for 383 days and counting, beating Mike Fincke, a two-time space station resident, who was the previous record holder at 382 days.

Breaking such a record for time in space is vital for Nasa's research into finding out how a trip to Mars impacts the human mind and body.

'Records are meant to be broken. Look fwd to one of my colleagues surpassing my end 500+ days on our #JourneyToMars,' Kelly tweeted today.

In this July 12 photograph, Kelly is seen inside the Cupola, a special module which provides a 360-degree viewing of the Earth and the space station. On each additional day he spends in orbit as part of his one-year mission, Kelly will add to his record and to our understanding of the effects of long-duration spaceflight

Station Commander Scott Kelly passed astronaut Mike Fincke, also a former station commander, on Oct. 16, 2015, for most cumulative days living and working in space by a Nasa astronaut (383 days and counting). Kelly is scheduled to come home March 2, 2016, for a record total 522 days in space

Kelly is set to break another record October 29 on his 216th consecutive day in space, when he will beat astronaut Michael Lopez-Alegria's record for the single-longest spaceflight by an American.

Lopez-Alegria spent 215 days in space as commander of the Expedition 14 crew in 2006.

The 51-year-old launched on a Russian Soyuz spacecraft from Baikonur Cosmodrome in Kazakhstan on March 27 and is scheduled to return to Earth on March 2, 2016, for a total of 522 days in space.

Waiting for him is his girlfriend of seven years, Amiko Kauderer, who is in Texas, working as a public relations officer at Nasa.

Kauderer snapped this photograph of herself saying goodbye to her boyfriend of five years, Scott Kelly, who is currently on the ISS

The 'One Year Crew,' consists of Commander Kelly (left) and Russian Cosmonaut Mikhail Koneinko (right). Each additional day in orbit as part of the one-year mission along with cosmonaut Mikhail Kornienko, Kelly will continue to add to his record and to our understanding of the effects of long-duration spaceflight

Scott Kelly's trip is designed to test how the human body copes with prolonged space travel.

Nasa is planning to compare Kelly's health to that of his identical twin brother, retired astronaut Mark Kelly, who has remained on Earth.

Called the 'Nasa Twin Study', the Kellys will be subjected to 10 experiments in four areas: human physiology, behavioural health, microbiology and molecular.

Mark who is married to former Congresswoman Gabrielle Giffords, says he has no intentions of consuming bland space-type food or working out and running two hours a day on a treadmill, as his brother is doing in space.

'This is a chance in a lifetime,' said Dr Craig Kundrot, the deputy chief scientist of Nasa's Human Research Program.

'In this case we've got two genetically identical individuals and we can monitor what kind of changes occur in Mark in an ordinary lifestyle and compare those to the changes that we see in Scott.'

By staying on the station for 12 months, the astronauts will also provide key information on how an eventual Mars mission - estimated to last three years there and back - might play out.

A mission to the red planet will require long periods of time in reduced-gravity environments, both in space and on the surface of the red planet.

But, until now, crew members have only spent about six months on the Space Station at a time.

Kelly is not the only human breaking records for time in space. Expedition 44 commander Gennady Padalka broke the 10-year-old record for the number of cumulative days in space June 28, as he reached 804 days in space.

The second image was posted last month and said: 'Good morning Texas! Great view of you, the moon, and Venus this morning.' Texas is seen to the right of the ISS, the moon and Venus are pictured bottom left

Blue veined landscapes have also been captured by the astronaut in the magnificent pictures posted to twitter on Monday

When he returned to Earth September 11, Padalka had spent 879 days living and working in space.

As well as carrying out numerous scientific experiments on the ISS, Kelly has been a prolific photographer.

Earlier this week, he captured a series of ethereal images of Australia from his lofty perch on the ISS.

The photographs make the country appear to be covered in sapphire coloured rivers, red veined mountain ridges and yellow lakes.

With a likeness to cells under a microscope the breath-taking photographs give an almost eerie representation of Australia.

This week, he also demonstrated what water looks like in space by popping an Alka-Seltzer tablet into a dyed globule of water.

Scientists at the International Space Station carried out the experiment to test their brand new camera.

THE YEAR-LONG ASTRONAUTS

Scott Kelly

This is the fourth spaceflight for Mr Kelly, 51, a former Nasa shuttle commander and Navy test pilot whose identical twin brother, Mark, also was chosen as an astronaut in 1996.

The two will conduct many of the same medical experiments over the coming year so scientists can compare the results.

Scott Kelly's first two flights were aboard shuttles. He spent more than five months on the space station in 2010 to 2011. It was during that mission that his sister-in-law, then Congresswoman Gabrielle Giffords, nearly died after being shot in the head in Tucson, Arizona.

Once he's back home in Houston, Kelly imagines it will be 'hard to walk away' from spaceflight.

He'd love to pilot one of the new US spacecraft in development.

But he figures if he cuts in front of other astronauts awaiting assignments, 'someone will run me over with their car.'

What will Kelly miss the most, besides his loved ones? The weather.

'It never changes on the space station,' he said.

'Even though it's a pretty nice environment, I guess it's like living in Southern California, people get sick of it ... after a while.'

Mikhail Kornienko

It is the second space mission for Mr Kornienko, 54, a former paratrooper whose helicopter-pilot father was part of the search and rescue team for the first Soviet cosmonauts back in the 1960s.

His father brought back souvenirs from the returning Soyuz capsules: uneaten food rations and pieces of the orange silky parachutes used for the final descent.

'Mom made gorgeous skirts out of them,' he said. 'I still have a small piece of one of those parachutes.

'I cherish it as if it were something sacred.'

A religious man, Mr Kornienko is taking into orbit a folding icon depicting the Madonna and Child.

His previous station stay was in 2010, 12 years after his selection as a cosmonaut.

He figures he'll miss the same things he dreamed about last time he flew: water not in the form of blobs as in space, but water you can swim in, as well as grass, forests and fields.

Mr Kornienko already says he'd take on another one-year mission — after a break, of course.

Scott Kelly (right) and his identical twin brother, retired astronaut Mark Kelly (left) pose for pictures during a press conference at the Baikonur Cosmodrome, Kazakhstan in March

Posting this image on Twitter, astronaut Scott Kelly wrote: 'Day 166. #Venus photobombed the #Moon tonight. Good night from @space_station! #YearInSpace.' This image shows the curvature Earth, the moon and Venus behind it as well as part of the International Space Station in the foreground

Scott Kelly tweeted a message about his record-breaking adventure earlier today, saying 'records are meant to be broken'

Nasa's brand new RED Epic Dragon gadget is capable of capturing resolutions up to 4K - four times the resolution of normal HD camera.

The video shows a ball of water floating around the gravity-free space station.

He then injects a drop of blue food dye into it, before adding some red dye, which turns the water green.

The 'One Year Crew,' consists of Commander Scott Kelly and Russian Cosmonaut Mikhail Koneinko, who are specifically investigating the medical, psychological, biomedical challenges faced by astronauts during long-duration space travel.

The international space station has been occupied since November 2000 and in that time, more than 200 people from 15 different countries have visited.

Crews are usually assigned 35 working hours a week and conduct research in different disciplines to advance scientific knowledge of the Earth space, physical, and biological sciences.

'What makes this exciting for me, this one-year flight, is about the science and everything we're going to learn from expanding the envelope on the space station,' Kelly said in an interview in December.

'If we're ever going to go to Mars someday, the International Space Station is really a great platform to learn much more about having people live and work in space for longer durations.

'It's close to the Earth, and it's a great orbiting facility.'

Kelly, a former Navy fighter pilot, said his goals are the same as they are every time he flies in space: 'No one gets hurt, we don't break anything and we leave as friends.'